text:
Closest RL Match for Fictional Helicopter Design?
Erm, not sure if this is the best place to post this but it seems like the best place to get a pretty straight answer thus far in my search.

So yeah, this helicopter is obviously from a cartoon – but I'm writing a story and I wanted to refer to it more specifically if possible, and also I'm just plain curious about what real rotorcraft(s) it was most likely based off of. And so far the entire rest of Google has not been much help. Plus, I've tried comparing some of the era models (i.e. 1960s, 1966-1968) I've found pics of on my own – but yeah, I am pretty clueless here. =(
Can anyone help? Thank you so very much for your time!
EDIT: I mentioned the year and I put the source in the pic description, but I'll reiterate both here. It's Michi/Trixie's helicopter from the Japanese anime Mach GoGoGo/Speed Racer 1966-1968.

Might help if you told us the cartoon/comic and the year that the cartoon came out so we can compare aircraft of a similar era and maybe even region.

Edited with necessary info more clearly marked. =)

Possibly the Bell 47J:

Source: Wikipedia
The Bell 47 was configurable with floats more in-line with the image originally posted, but I can't find a lot of images with the full skin frame and floats, but here is one:

Source: Goodall Aircraft History

Aaaah, that looks incredibly similar, even down to the design in the first pic minus the colors! This definitely works. OMG THANK YOU SO MUCH ❤

Yeah that's it.  By the mid 60s it would have been the most recognized helicopter in the public's mind from TV and movies so I would have expected a cartoon to be a likeness of a '47 J.

The bulbous design makes me think of the MD500, although the tail of that, like most helicopters, comes from the top of the body, while your cartoon image has the tail connecting at the bottom.


text:
Which commercial aircraft can fly Micro-SLOP procedures?

"Strategic Lateral Offset Procedures (SLOP) are approved procedures
  that allow aircraft to fly on a parallel track to the right of the
  centre line relative to the direction of flight to mitigate the
  lateral overlap probability due to increased navigation accuracy and
  wake turbulence encounters."

ICAO 4444 Pans ATM 16th Edition section 16.5 Note 1.
SLOP of one or two nautical miles has been recommended for use in oceanic and
remote continental airspace for a long time. For example, the North Atlantic Track (NAT) system has permitted SLOP since 2004 and has been a mandatory requirement to fly SLOP over the North Atlantic since 2017.
In the 16th Edition of ICAO 4444, published in 2015, ICAO extended the use of
SLOP to en-route airspace in tenths of a nautical mile up to a maximum of 0.5NM,
i.e. Micro-SLOP.
This change was originally proposed in ICAO Circular 331 to counter the effect of the navigation paradox after the mid air collision over Brazil in 2006, see Gol Transportes Aéreos Flight 1907.
Currently, Micro-SLOP may only be applied on routes promulgated in AIPs by aircraft equipped with the appropriate automatic offset tracking capability.
Most ANSPs do not permit Micro-SLOP in their AIPs. However, the NAT recommendations have recently changed to recommend that pilots fly Micro-SLOP over the North Atlantic, see Two is not enough.
My pilot friends tell me that small commercial aircraft fitted with the Universal Avionics SCN 1000 and 1100 FMS's can fly 0.1NM offsets but that Airbus A320's can only fly offsets in 1NM increments.
The question is: which commercial aircraft currently have the capability to fly Micro-SLOP procedures with route offsets of only 0.1NM?

Welcome to Av.SE! Interesting question.

According to the below references, these commercial aircraft are capable of doing the Micro-SLOP procedures with 0.1 NM increments:

INTERNATIONAL FEDERATION OF AIR TRAFFIC CONTROLLERS' ASSOCIATIONS 58TH ANNUAL CONFERENCE – Conchal, Costa Rica, 20-24 May 2019

2.6.2 Most flight management systems in service today can execute an automatic offset track in whole nautical miles. Unfortunately, as offsetting by tenths of a nautical mile was only introduced in ICAO provisions in 2014, most flight management systems are currently incapable of executing such offsets. Of the major aircraft and flight management system combinations in production, only the Boeing BBJ, 737 and 787 are currently capable of offsetting in tenths of a nautical mile. Depending on the aircraft mix in the airspace, even if a State permits offsetting in tenths of a nautical mile, the majority of aircraft may not be able to participate in this SLOP, and the full benefits may not be realised.

Cir 331 A /192N Implementation of Strategic Lateral Offset Procedures ICAO

1.3.8 The idea quickly emerged to employ the capability of some modern aircraft to offset in fractions of a mile for this purpose. Both Boeing and Airbus announced that all their future aircraft would have the capability to offset in tenths of a mile and it was therefore clear that using such “micro-offsets” to mitigate the collision risk would be viable in the future.

IFALPA (International Federation of Air Line Pilots’ Associations) Saftey Bulletin (NAT Lateral ASEPS)

Micro-SLOP is currently authorized throughout the NAT region. The latest information available to ALPA is that the most recent Boeing B737s (NG, Max), B787s, and the B777X (when it enters service) have Micro-SLOP capability. Airbus is planning an enhancement across their product offerings in the 2022+ timeframe. There is no hazard introduced by this mixed implementation of Micro-SLOP.

I know I'm not supposed to say thank you... but thank you. That's precisely the kind of answer I was looking for! I wonder why Airbus is so far behind Boeing on this?

source: Stack Exchange

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sort: votes


text:
What is this thing on the engine of a Cessna 500 Citation I?
I've noticed something on the engine of this bizjet. Could somebody explain what that is?

Source (image modified to indicate location of fairing).

Those are the fairings containing the mechanisms for the engine's reverse thrust system. See this photo (copyrighted) of the similar reverse thrust "buckets" deployed on a Citation 550.
See this example of a similar thrust reverser system deployed on a different aircraft type:

Image source, public domain
See also Wikipedia's article on Thrust Reversal systems.

A common name for this is a "stang"

@SteveH A "stang fairing", yes, you're right.

Copyright image nicely handled!

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/

authors: Евгений Балахнин


text:
What is an accessory gearbox?
Many 737 engines have an accessory gearbox on the 9'o clock position, which is part of why the engine has a flat-bottomed shape. What exactly is an accessory gearbox?

Related: What is the different between an aircraft engine gearbox and an aircraft engine transmission?

The accessory gearbox is generally driven by the N2 shaft (connecting the high-pressure turbine to the high-pressure compressor) and in turn drives the engine accessories such as generators, hydraulic pumps, oil pumps, etc.  The air turbine starter is also part of this gearbox so during starting the accessory gearbox drives the high-pressure compressor.
This analogous to the serpentine belt on your car, which connects your crankshaft to your cars engine accessories (alternator, water pump, power steering, air conditioning, etc).

From this answer, an accessory gearbox for the Rolls Royce Trent. The accessories connected to the engine spool(s) are:

The Engine Driven hydraulic Pump
Fuel pump
Oil pump
Pneumatic starter, requiring the highest loads and therefore dimensioning the gear strength.
The IDG: Integrated Drive Generator which provides the AC power.

Only the pneumatic starter must be connected to the HP spool. The other accessories may be connected to the LP spool, which turns at lower RPM.
The Accessory Gearbox can be placed relatively freely along the engine outer radius: on top, underneath, or to the side as in the B737.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/

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text:
Where are the flap track covers on this wing?
I don't see it has covers for the flap tracks, so,where are the covers for the flap tracks?

Image taken from the English for Aviation book (Oxford).
The aircraft is a Vickers VC10

It appears the shock bodies aren't being used for the flap tracks, as the flaps are only between them and not over them. So there is nothing to cover.

But wouldn't that result in drag?

the shock bodies will increase the wet surface and the friction drag but they reduce the wave drag, netly is interesting to include them

So the flap tracks are uncovered,  that means the wing will have drag? Is it inefficient to have flap tracks uncovered?

Well yes, if they are not faired, they will add drag... but if we're talking about the pictured wing, we can't see the flap tracks so we don't know how much.

Mmm yeah. I'll try to figure out which plane is that one.

Yes. It's a Vickers VC10

As a side comment, it looks like the aircraft is jettisoning its fuel.

From the Vickers VC-10 repair manual:

General arrangement of VC-10 wing (picture source). Note the labelling of the Shock bodies as "flap rail fairings".
The flap tracks were inside the Küchemann bodies and the flaps were between them. This produced gaps between the five flap segments which made them less effective than the modern design of uninterrupted flaps with the flap tracks below them.

They look like Fowler flaps, like on Hercules c130. If that's the case the flaps run on screwjacks and rollers and slip up and into the wing when cursing. All the mechinisums are shrouded by the flaps themselves when retracted and hence no drag. On takeoff and landing the drag is overcome by takeoff thrust and on landing augmented by airbrakes to reduce landing speed. The flap tracks are in the wing and accessable only when the flaps are extended/ deployed.

Gotta love "cursing" around in an airplane!


text:
Why are passenger cabins white?
Almost every passenger cabin in a commercial aircraft is white with a little bit of grey. Why are they in these colors?

Source

The orginally colour of plastic are nearly-white/colourless

because sitting in a bright orange room for 8 hours would drive passengers insane.

Why are the rooms in most houses painted white?  Because it's a nice neutral color, and reflects light so you need less interior lighting.

Check out this article on the innovative effects of colored lighting in the 787. The are also several videos on YouTube about it

If you want to know the effect of lighting, just ask a picky lady about how her clothes/makeup looked just right at home, but are horrible now that she's out in the sunlight/office/night club. While fashion isn't the primary goal in cabin lighting, anything non-neutral will throw off perceptions which will range from moderate annoyance (colors don't look right in the in-flight magazine) to downright dangerous (finding the emergency exits in a red interior).

The picture in your question shows the answer: Most lighting in the cabin is done indirectly, so you don't see the light source directly. Instead, light is reflected off the cabin interior. If you would paint that interior in gaudy colors, you would have undesirable effects. Colored surfaces absorb some wavelengths, so the brightness in the cabin is reduced. Plus, the selective reflection will shift the color of the light.

Newspaper and magazine paper would not be white anymore, but have the color of the cabin interior. As @mins correctly points out, the brain can compensate for this. It will, however, make it difficult to read text printed in the color of the cabin interior because it would no longer stand out from the background.
The color pictures in the magazines would look funny. If you now think people could switch on the reading lights: Note how few passengers actually know how to operate them.
The food you get served would look funny. It is already not a pleasure to look at in most cases, but in colored light it gets even worse.

While it might be fun momentarily to be in a room with mood lighting, being exposed to this one color for the full length of the flight without a possibility to escape (except for closing your eyes) will offend most passengers.

Just a detail: Actually our brain is able to do a "white balance" after some time without us being aware, so white paper will still be perceived as white. I don't know what is the color spectrum of our light at home, but it's probably no the same than mine, and it doesn't matter for color perception (if the spectrum is not too much degraded) This phenomenon creates visual artifacts of the complementary color when the object is removed, due to the previous "white balance".

+1 for "The food you get served would look funny. It is already not a pleasure to look at in most cases, but in colored light it gets even worse.."

Although not the original reason, modern plane interiors are designed to keep people calm. Boeing has a nice article on it here that is worth taking a look at.

Color psychology plays an important role in developing the overall
  look. Studies show that people in different cultures associate certain
  colors with similar emotions or concepts. Blue/green is nearly
  unanimously associated with peace. Pink and lavender shades connote
  love, while blue/purple may signify nobility.

The darker colors of seats can also aid in hiding stains and dirt better than say white or tan leather (which is found in a lot of GA planes).
As has also be mentioned in some of the comments white plastic is how most plastics are made thus its most likely cheaper to order something in white than have it colored.
There are some emergency implications to interior colors. In the case of an emergency you want the exits to be clearly marked and easy to find. If you have a "busy" interior when it comes to both over all design and color you can have issues making an emergency exit that contrasts well enough to see when it needs to be seen.
For what it's worth color has been tried (then again, it was the 70s). Now think about a red emergency light going off in this plane, it would barely stand out.

(source)

Are you sure this is a picture from an actual plane? Looks like the Village People are about to start singing... :-)

@jcaron That is Braniff International Airways

I love the cabin crew uniform.

The 60s were a bit different...


text:
When is an aircraft required to be pressurized?
For example a Cessna Grand Caravan doesn't have a pressurization system, but a Phenom 100  is pressurized, so what are the main reasons a manufacturer has to build an aircraft with a pressurization system: altitude, speed, etc?

In the United Kingdom it is a legal requirement to carry supplementary oxygen above 10,000 ft, whether that is an oxygen mask or pressurised.

The main reason is that it's simpler than having everyone wear supplemental oxygen masks. There is no specific requirement for pressurizing an airplane but there are requirements for supplemental oxygen as per FAR 91.211

(a) General. No person may operate a civil aircraft of U.S. registry--
(1) At cabin pressure altitudes above 12,500 feet (MSL) up to and
  including 14,000 feet (MSL) unless the required minimum flight crew is
  provided with and uses supplemental oxygen for that part of the flight
  at those altitudes that is of more than 30 minutes duration;
(2) At cabin pressure altitudes above 14,000 feet (MSL) unless the required
  minimum flight crew is provided with and uses supplemental oxygen
  during the entire flight time at those altitudes; and
(3) At cabin pressure altitude above 15,000 feet (MSL) unless each occupant of > the aircraft is provided with supplemental oxygen.

So by pressurizing the plane to under 15,000 ft you can fly over that altitude and not need to supply the passengers with supplemental oxygen for the duration of the flight. There are unpressurized piston planes that fly well into the flight levels but are required to carry supplemental oxygen and everyone aboard needs to use it, it's a look some people in general aviation don't mind,

(source)
On a slight side note the engine does have an effect on this choice when it comes to light singles. Pressurization systems on turbo props/light jets pull their air from the compression stage of the turbine which is already compressing air so no extra compression hardware is needed. If you have chosen a piston engine for your design you need to drive some form of pressurization system which can add weight and complexity. There are a few pressurized piston planes out there like the Mooney Mustang, Cessna 210 (came in both pressurized and un pressurized) and the Piper M350 (the only one currently in production).

Also note that sailplanes can easily reach altitudes well over 14K ft, yet very few are pressurized.

Isn't temperature also a factor at higher altitudes?

Every small GA I have flown in (and can think of) has cabin heat with the limited exception of things like a Piper cub (which cant really even go that high). Its now becoming common for planes in this class (CSR22, Mooney Acclaim, Piper Matrix) to come with De-Ice equipment standard or as an option.

An aircraft is never "Required" to be pressurized. The only reason to pressurize an aircraft is profit.
No one would ever buy an un-pressurized Phenom 100 or B777, but there is nothing stopping you from building one.
Pressurized aircraft are built because they can generate a profit for the manufacturer. Any aircraft can be made with pressurization but it comes with a price. If marketing determines it will sell, they will build it with pressurization.
You can look at pressurization as simply a comfort option. A comfort option that comes with a price.
There have been many cases of aircraft being built in both pressurized and un-pressurized versions.
The Cessna 402 and 414, Cessna 335 and 340, Cessna 210 and P210, Piper PA-31 Navajo and PA-31P Pressurized Navajo are all examples of the same aircraft built in both pressurized and un-pressurized versions.
In all these examples the un-pressurized aircraft can fly well above 20,000' but is generally operated at lower altitudes due to the inconvenience of using supplemental oxygen.

Spot on. I appreciate this perspective.

Generally, the operating altitude of the aircraft determines whether the aircraft is pressurised or not.
Regulations require the pressurised cabins to maintain certain perssure at the maximum operating altitude. For example, FAR 25-841 Pressurised cabins requires the cabin pressure to be maintained at 8000 ft at the maximum operating altitude of the aircraft.

(a) Pressurized cabins and compartments to be occupied must be equipped to provide a cabin pressure altitude of not more than 8,000 feet at the maximum operating altitude of the airplane under normal operating conditions.

Thought there is no set altitude of operation for the aircraft to be pressurised, it is required to provide supplemental oxygen if the pressure altitudes are above 12500 ft:

§91.211   Supplemental oxygen.
(a) General. No person may operate a civil aircraft of U.S. registry—
(1) At cabin pressure altitudes above 12,500 feet (MSL) up to and including 14,000 feet (MSL) unless the required minimum flight crew is provided with and uses supplemental oxygen for that part of the flight at those altitudes that is of more than 30 minutes duration;
(2) At cabin pressure altitudes above 14,000 feet (MSL) unless the required minimum flight crew is provided with and uses supplemental oxygen during the entire flight time at those altitudes; and
(3) At cabin pressure altitudes above 15,000 feet (MSL) unless each occupant of the aircraft is provided with supplemental oxygen.

Basically, the aircraft designer has to decide between pressurising the aircraft (which increases weight and complexity) and having a non-pressurised fuselage and operate at a lower altitude, where the performance may suffer (or provide supplemental oxygen). It is a tradeoff and the decision usually depends on the aircraft design requirements. Note that pressurised aircraft also have to be provided with supplemental oxygen above FL250.
For example, the Cessna Grand Caravan operates at a cruise altitude of 12,000 ft, has an unpressurised fuselage, while the Phenom 100, which operates at a higher altitude has pressurised fuselage.

The requirement for a pressurization system is dictated by the operating altitude. With increased altitudes the atmospheric pressure diminishes and so the concentration of oxygen available.
T o have an idea of what is consider a "critical altitude" for an average human we can have a look at FAR 91.211. It requires to  use oxygen when flying above 12500ft (3800m) for more than 30 minutes, and in any condition about 14000ft (4300m).
The CS-23 certification requirements, which applies to aircraft 12500lb (5760kg) state the following for pressurization systems:

CS 23.841  Pressurised cabins
  (a)  If  certification  for  operation  over  7620m
  (25 000 ft) is requested, the aeroplane must be able
  to  maintain  a  cabin  pressure  altitude  of  not  more
  than  4572m  (15 000 ft)  in  event  of  any  probable
  failure or malfunction in the pressurisation system.

These are the requirements a different aspect is what a manufacturer selects for its design which be influenced by other factors such as:

Comfort
Marketing
Safety

The problems of high altitude are nothing to do with the mechanics of inhaling, it's simply because when the air has lower pressure and density the amount of oxygen available to be absorbed is less. If it were about the physical effort, it would be much harder to accidentally fly into a situation where hypoxia is a danger.

@DanHulme, thanks, corrected!

Aircraft do not need to be pressurized.
Above about 12,000 feet humans need additional oxygen.
Above about 50,000 feet any humans inside the aircraft need to be wearing pressure suits.
There is no "requirement" for any aircraft to be pressurized.

Taking a broader view.
If the "partial pressure" of oxygen (that is the overall pressure of the gas mixture multiplied by the propotion of oxygen in it) in the gas mixture people are breathing drops too low then people will suffer serious and potentially life-threatening medcial problems. We need to prevent that happening. There are several options for preventing it each with different disadvantages.
One option is to simply fly low enough. This is a common soloution for low speed travel but it doesn't work well for high speed flight. It may also cause issues if you need to fly over mountains.
A second option is to have everyone use supplemental oxygen delivered through some form of mask (possiblly a full face mask, possiblly a non-sealed mask like the one in Daves picture). This is an option for military planes and some GA stuff but I don't think it would work too well for airliners or buisness jets.
The third option is to pressurise the cabin. This allows you to fly at high altitudes where fast flight is practical while providing an environment where people don't have to tether themselves to oxygen masks. The downside is that your fuselage is now a pressure vessel and worse it's a pressure vessel that experiances frequent pressure cycles. As a result pressurised airplanes require far more careful design, construction and maintinance then unpressurised ones.
A fourth theoretical option would be to use an oxygen enriched atmosphere in the cabin. Afaict this is not used in avaition, I don't know exactly why but I would guess a combination of fire risks and the difficulty of supplying enough oxygen.


text:
Why did this departure from Buenos Aires seem to delay heading northeast?

It was going from Argentina to Germany and after takeoff it went over a town and then it went direct to Germany. Why did it go over the town instead of going directly to Germany?
Source

Which runway did you takeoff from? 11?

@aeroalias Yes I think so.

It's following a departure procedure.

(chart source)
The path flown matches the route described for departing Runway 11 with the La Plata 6B departure.
See the map here to visually match up the described departure procedure with the flown path.

The reason this SID is designed this way? Noise prevention and not overflying Buenos Aires?


text:
Why are modern commercial airplanes still so noisy?
After years of scientific research on the performance of commercial aircraft like 777's or A320'S, the cabin noise is still very loud. Modern aircraft have new features like serrated engine nacelles, like on the 747-8 or 787 engines; improved aerodynamics; vortex generators; cabin insulation, etc. So why do aircraft still have so much cabin noise after all these improvements?

I think the premise here is questionable.  Stand outside near a running jet engine, and you'll appreciate just how much the noise IS reduced inside the cabin!

There is only so much they can put on the airplane with the space and weight limits. Still they reduce the noise by plenty.

Perhaps for essentially the same reason that people in tourist class are packed in like sardines: because they'll tolerate it and it allows the airline to make more money.

How quiet do you expect that 550mph wind on the other side of the window to be?

The quietest jet aircraft I ever flew on was an Air Force C-141. But that was on the flight deck. Having spent a lot of air time in both military and commercial aircraft, I can say that the commercial versions were always quieter in the passenger area. However there are certain zones that will always be the loudest ... the point where you're at about a 45 degree angle to the intake or exhaust. I always prefer sitting in an aisle seat over the wing root, but that's just me.

Go fly a glider. You'll be surprised how much wind noise there is.

If we were to achieve full noise isolation in the future, would we do it?

Like everything in aviation its a trade off of a few factors.
Efficiency: A non-running engine is pretty quiet but that's of little use to a pilot who needs thrust to actually go anywhere. Now you can have lots of sound suppression in an engine and alter the airflow and what not but in the end of the day jets work on Newton's third law so you still need to throw a hot mass out the back. Any attempt to baffle this will take a toll on efficiency. (Side note, car exhausts have a similar effect on car engines these days).
Weight: The generally accepted way to reduce noise is to insulate against it. What you are really doing is adding material to absorb the mechanical energy that is the sound wave and dissipate it. Generally this is done with insulation of some kind (there is a variety of styles). But like anything this takes a toll on weight and will reduce what you can carry.
Cost: Insulation does wear out and break down over time (its usually some kind of foam), so the more you have the more you need to replace. Also of importance is the fact that most of it gets removed during check to inspect the airframe so having a lot of insulation will add to your down time during checks (this costs the airline money in terms of hours).
If you take a look at some custom-built private planes you will see some of the things they can do in terms of added noise reduction and what those implementations look like. On the other hand active noise control is becoming a cheaper and more efficient technology in headphones which makes a case for not needing to improve insulation (it will eventually be cheaper to have a pair of ANR headphones for everyone than maintain a lot of insulation). A lot of the GA community has moved to ANR headsets which are much nicer than their traditional counterparts.

I was flying in a friend's twin engine airplane one day and he had a spare headset with ANR. It was like the engines had shut down.


text:
Is it true that the red lights on building antennas help the aircraft "detect/visualize" ground objects?
I was thinking that red lights on the antennas on buildings help aircraft to see if there are tall objects in the ground. Is this right?

Source

Try this. Synchronize your eyes to the blinking of the lights such that you never see them on. While maintaining your blink speed and duration, spin around in a circle (slower makes it easier for you). When you get back around, find the tower. At night, this is really, really, really hard. Imagine doing that in an airplane...

@corsika I don't understand the point of the blinking and spinning exercise.

No, the red lights are for the pilots to see.  Very few aircraft (maybe some drones?) are capable of seeing things.

@JonathanWalters You're trying to see what the towers look like without the lights on. It's a lot easier (and fun!) to just synchronize your eyes to their blink such that you never see the lights on than it is to actually turn the lights off. Also safer. You spin around so it's harder to cheat from when you saw the lights on. Bonus: once you play around with it, you can play games with the lights and have them shoot other lights!! Takes a while to learn how but once you do it's super fun.

@corsika Is the exercise supposed to contribute to situational awareness or collision avoidance, or is it supposed to be for amusement? Personally, I find towers and windmills to be deadly serious matters.

Seems fairly obvious to me that the purpose of the exercise is to demonstrate a concept without having to actually get in a plane.

@JonathanWalters It's to illustrate why those lights are so important - the things they illuminate are very difficult to find even if you know there's something to look for. The fact that you can use them for entertainment when a passenger on long roadtrips is just a bonus feature.

@corsika OK, in other words, an unlighted building or tower is hard to see...

At a smaller general aviation airport, you can take a demo flight. If you can take one at night, you'll see how it works. If it's clear you can see these from quite a distance.

It surprises me that nobody pointed this out yet, but beside the obvious safety reasons these lights can prove quite useful for navigation under certain conditions. "My" three towers around "my" airfield help me a great deal for the first rough line-up, especially in dim light.

Those lights are used to show obstacles that may interfere with the aircraft's course, such as antennas, buildings, wind turbines, and they are mandatory.
The name of those lights is Aircraft Warning Lights, and here is an article from Wikipedia about them.

I was in a city-wide power blackout once (rain flooding the electrical substations), and it was notable that (apart from a hospital and car headlights) the only signs of electricity were those aircraft warning lights on (all) the tall buildings ... i.e. fwiw they're important enough to have backup (battery or generator) power.

@ChrisW: In a lot of countries they are so important that they are run by dual backup batteries, sometimes plus generator and every light you visually see is run by at least two bulbs.

I've seen the control panel for one of these "lights" in a water tower, and it's amazing how complex it is for a simple light.  Multiple redundancies and backup power sources.

@JPhi1618 it makes sense, since their failure leads to very, very big problems.

Lights are increasingly useful for situational awareness when visibility worsens for any reason (night, fog, rain...)

But they're a pain to change ;-) Cold fingers and hot bulbs :-(

The lights are also useful for any constructions near helipads, such as hospitals. I'd imagine helicopters are more likely to fly near ground/buildings than GA aircrafts.

Yes, the lighting is helpful for collision avoidance.
The red lights are helpful, but the white strobes can be even better for visibility.
When I am flying very low to the ground I am far more concerned about towers and windmills (or occasionally high tension power lines) than buildings. Fortunately all of my really low flying for work is done during daylight hours, but in heavy overcast or other low-light conditions the lights are very helpful.
Most tall buildings are in congested areas and most flight operations will be required to maintain an altitude of 1000 feet or more above such structures. The presence of towers in excess of 500 feet, and especially in excess of 1000 feet, in uncongested areas posses a much more credible threat to VFR low level flight.
The FAA describes the standards for structure and tower lighting in AC70/7460-1L. Generally, any structure that exceeds 200 ft AGL should be marked and/or lighted.
Note that, though the lighting may be mandatory, it may be NOTAMed out of service.
For example:

!SFF 02/009 SFF OBST TOWER LGT (ASR 1060807) 473535.00N1171750.00W (5.5NM S SFF) 3971.1FT (352.4FT AGL) OUT OF SERVICE

Could you unpack or link “NOTAMed out of service” for the novices among the readers?

@sevensideddie Good idea, standby.

NOTAM stands for "NOtice To AirMen", and is an official notice filed with the local, regional, or national aviation authority to alert pilots of hazards or other deviations from normal protocols along their flight path.

Before the lights were installed, this happened...

(second picture via Pinterest)
A better picture of this incident (a 1915 Sopwith Baby at Horsea Island in 1917) appears in the front of the 1925 edition of the "Admiralty Handbook of Wireless Telegraphy" in a slightly snarky advert, captioned "A proof of the quality of Elwell masts".

Also, in NYC this happened.

To answer your question directly, no, they are not used to indicate that you are too close to the ground.  Some of them are over 1500 feet high.
They are used so you do not fly into them for obvious reasons or fly too close to them for less obvious reasons:

Some are powerful transmitters and can interfere with the systems on the aircraft.
Towers often have support wires which extend a long way from the obstacle with the light and do not have lights themselves.

Too close to the ground is figured out by looking; by the altimeter; by charts and by planning.
The red light just means "keep away!"
Some incidents and analysis of interference and even crashes attributed to high intensity EMR.
Some follow up on the Blackhawk crashes.
Whilst this paper focusses primarily on the ability of high powered EMR sources to cause ignition sparks up to 30kms away (!), it also shows how dangerous they are up to hundreds of metres away.
If anyone remains unconvinced that powerful transmitters need to be avoided by aircraft, please let me know and I'll do some more digging, but for now, I have an "all nighter" I need to pull to deliver a project tomorrow so I may be some time....

"Some of them are over a kilometre high."
I have never heard of an obstacle over a kilometre tall.  The world's tallest antenna is only 600m tall.

Some are powerful transmitters and can interfere with the systems on the aircraft. Has this ever been documented to occur?

Personally, I have flown quite close to some of the transmitters (I don't know how powerful though) without any negative impact to aircraft systems. Such proximity would only be possible in VFR flight, where any possible system impact would be negligible for safety of flight.

A "drive by downvote" with no comment.  I couldn't care less that I've lost a whole 2 rep points, but it really grates me that I can learn nothing from it.

@abelenky  Sorry, a simple typo which I fixed at the same time you where typing your comment.

@TomMcW Yes. I'm searching for references, both to the occurrences and to the guidelines which specify separation distances.  I'll edit to include.

@JonathanWalters So because you have not experienced being struck by lightning, it doesn't happen?  We're not talking about PEDs here.  We're talking multi-megawatt transmitters which generate significant harmonics and EMR on multiple sidelobes powerful enough to be dangerous, in some cases up to hundreds of metres.  Many transmitters have "no human" zones when radiating.  What leads you to conclude that such proximity can only occur when VFR?  I don't get that at all.  For example, IFR flights into London were, until it was retired, routed away from the old Crystal Palace TV transmitter.

@Simon I'm only sharing my personal experience. The proximity I am referring to would not be possible in IFR flight. And I did not downvotes fwiw.

@Simon Glad to see you've recovered from your Corsair hysteria. Here's an upvote to counter that drive-by

@Simon:  I did not drive-by-downvote.  Your original post claimed obstacles over a kilometre, which is just unrealistic.  I commented, and down-voted for an answer not based in reality.  I would now remove my downvote, but it is currently locked. Don't pretend it was a drive-by when my comments are clear and timestamped.

@JonathanWalters Why?  Are you assuming that IFR traffic is only ever where it should be?  I also know you didn't downvote, I "virtually" know all the main players on here and it's not how we behave ;)

@abelenky I didn't think it was you which is why my comment was not addressed to anyone.  Don't worry about reversing it, I really don't care, but thanks for letting me know that was the reason.  You might consider adding "-1" so people know, otherwise, I have no way of knowing and therefore, it's a drive by.

I suppose I am making that assumption. To be clear I am talking about positions within 100 ft of the transmitter and at a level with, or below it.

@JonathanWalters Yep, that's the problem area, actually, for the big TV transmitters, the danger zone can extend beyond 100 metres. I am determined to find the relevant links.  (BTW, ex-avionics engineer and I know the problems caused by powerful EMR which need very special attention to be paid to shielding and antenna designs usually not found outside military and big iron -e.g. missing in some bizjets and most GA)

OK, yeah, I would be very interested in more info on the transmitters since I have to fly pretty close to a lot of them for work.


text:
Do surfaces ahead of propellers decrease thrust?
I have had this question for ages, nearly impossible to find anything on the web. My experiments confused me even further! Its concerning the blockage effects of surfaces ahead of a propeller. For example lets  consider  the usual dual vectoring propellers on the sides of airshipcars like in the skyship 600 for instance.The gap between propeller disc and underside of blimp is 1diameter.
In vertical flight the propeller's  intake are faced by the underside of the blimp body itself. How are the propellers still able to generate thrust when the propellers' intakes are  "somewhat blocked" due the very close surface of the blimp?
As An experiment I  attached a foam sheet about  1.5 diameters above a big 28 lbs 8-rotored octo- multirotor in hopes to see that the multirotor would still lift.  At full throttle the multirotor  didnt even move or lift.  Obviously it lost almost all of its thrust due to the the sheet blocking the airflow above.. even though the foam sheet was high above the props,  about 1.5 diameters.
Can someone help me  on what could be going on here? does having a surface above  a propeller decrease its thrust? Why did my experiment showed different results than the blimp. Are there other factors involved? if so.. what is the relation between distance, disc loading, surface shape, other factors etc  and thrust decrease?
Thanks!
Best Regards
/Eric

does having a surface above a propeller decrease its thrust?

Anything that can prevent or reduce the acceleration of air will reduce the effective thrust of a propeller.  That might include obstructions in front of or behind the propeller.

Why did my experiment showed different results than the blimp.

First of all, I don't see any information about the blimp.  Perhaps it too is greatly affected.  I don't know how much thrust is required in this configuration.  It may be tiny compared to the thrust available when pointing fore-aft.  If true, both propellers have reduced efficiency.
Second, I would think there's a big difference between a flat obstruction and a smoothly curving one.  Your experiment would be closer to the blimp situation if you put a large blimp shape over the propellers rather than a flat sheet.

Second, I would think there's a big difference between a flat obstruction and a smoothly curving one. Your experiment would be closer to the blimp situation if you put a large blimp shape over the propellers rather than a flat sheet. <--- this right here!

I think I have a close answer:
I made more extensive testing for various new homebuilt multi rotors from 300grams weight to 14kg of several shapes, propeller sizes, and power/disc loading that have inbuilt airblocking "roofs". Got so frustrated with violently different results despite same dimensions until I found out the secret.
All tests were done with stand alone free flying machines with bolted on airblocking roof to eliminate any measurement errors. Power is  monitored with onboard sensors.
Landing gears are made extensively high to avoid any ground-deflected air interference.
Turns out that indeed finally as I originally suspected that the disc loading is the deciding factor. The low disc loading (8"-prop ) 400gram quadcopter showed zero reduction of thrust or efficiency due to air blockage at 1 diameter distance.
The big 13kg new quad copter(12"props) that now also had  air blockage at 1 diameter distance didn't even get off the ground. Thrust was drastically reduced to around 30-40% I would guess.
Blimps must be operating at lower efficiency but ofcourse I can never be 100% sure due to lack of technical paper on the subject.
Thanks


text:
Why are these windows on some airplanes red?
There are some red windows on the 737 and the CS-300 as well. Why are they painted red?
Source

Source

A red/orange color is typically used to denote flight test instrumentation. Indeed, these windows do contain such instrumentation. Below you can see a similar window on a 747-8I flight test aircraft (note the 7th window from the nose):

And the corresponding inside view:

What is in those big tanks?

@RockPaperLizard, those tanks hold water, which is used to create different center of gravity/weight conditions for flight test purposes.

Makes sense.  Thanks for the explanation.

The aircrafts shown above are test aircraft and the windows are blanked for mounting test instrument. The image below shows the inside of Bombardier C-series test aircraft, which shows the mounting of test equipment.

Image from airwaysnews.com
Also, the screengrab below from this video about C series testing shows the interior of the C series test aircraft with blanked windows with attached instrumentation.

Also, see this thread that discusses about the same thing.


text:
Is trigonometry used by commercial pilots?
Do pilots (for example commercial pilots) need to use trigonometry (directly, with trigonometry knowledge) as part of their routine job?
If so, when is it most used and for what?

Note that this answer was given to the original question, Do pilots need to use trigonometry as part of their routine job? If so, when is it most used and for what? The question was subsequently edited, after this answer was accepted. Much of the information provided in this answer does not now apply directly to the current question, but it does serve to provide context and for this reason it has been retained.

Pilots use trigonometry primarily for calculations involving wind angles, either for navigation or for cross-wind components for takeoff or landing. Note that pilots often accomplish these calculations with a flight computer such as the E6B, a circular slide rule:

Image by Dave Faige — Source — used under CC BY-SA 3.0
Many such flight computers are available, including electronic versions, such as the Sporty's electronic E6B. Personally, I now prefer to use web-based software, but in flight school my preferred calculation method was a TI-83 programmed to do vector addition and other pre-flight calculations. In the cockpit, the CR-3—a pocket version of the larger E6B mechanical flight computer and which can be operated with one hand—is usually the most functional method.
Regardless of how they are performed, such calculations are typically for the purpose of either:

Calculating wind correction angles for cross-country navigation based on forecast wind conditions, or
Calculating crosswind component for takeoff or landing based on reported wind conditions.

The later are fairly straight-forward; the former are more complex. Crosswind component is a simple tangent calculation. Wind correction angles are more complex involving vector addition taking into account magnetic course, true airspeed, forecast wind angle, and forecast wind speed.
Now, the original question was merely, do pilots need to use trigonometry. The answer to that question is, "Yes". The question has since been edited to specify the use of trigonometry "directly, with trigonometry knowledge". The answer to that question is, "No", pilots do not need to have a working understanding of trigonometry, though they do need to be capable of computing the above described wind problems. A pilot need not understand the trigonometry used by the calculator, slide rule, or FMS that he or she uses to perform these calculations. I know good pilots who have no real working knowledge of trigonometry and do quite well without it.
For a pilot flying in the IFR environment, wind correction calculation is less frequently a needed calculation since most navigational means provide for wind correction in some way. This is especially true of GPS or RNAV navigation, because the ground track can be compared to the aircraft's heading to show wind correction angle.

It's worth noting that the purpose of the E6B and wind component charts that pilots use are so that we don't need to know (or work) the underlying trigonometric equations: The tools we use are derived using trigonometry, so all we have to do is turn the dials and read the numbers. All the math is done for us.

@voretaq7 Right. We use it, albeit more or less indirectly. I have only rarely sat down and actually worked the trig for a wind problem. Hence why some (many?) pilots can work the wind problem using trig without actually knowing trig.

Agree with voretaq7 -- perhaps you should change the first line to say "Pilots use trigonometry, even if only indirectly..." or something like that.

@rbp "Pilots use trigonometry, even if they don't know it ".

@rbp I could, though as FreeMan pointed out the body of my answer does include that note. The real issue here is the question that I answered is not the question we now see at the top of this page; the question has been substantially specified and narrowed in scope, most recently with the addition of the commercial pilots and directly, with trigonometry knowledge parentheticals.

I think the best example of routine use of trigonometry by pilots is to calculate winds aloft.  The data a pilot has on hand is his compass heading and his airspeed and his altitude and his true bearing based upon passing landmarks on the ground.  From this data he can calculate the wind direction and velocity he is witnessing at his location and altitude.
Normally he would use a flight computer called an E6B which is a circular slide rule of sorts.  The E6B is easier to handle in turbulence than a pocket calculator.  I proved this to myself many years ago when I added a program to a programmable pocket calculator to do the computation.  It was hard to improve upon the time-tested E6B.


text:
How do pilots avoid radiation?
It is said that they are exposed to 50% more of radiation than on the ground and they are prone to skin cancer, so, is there any way of reducing the amount of radiation for pilots?

Avoid the sun. I'm not concerned about my flying activities causing harm, though. If I get skin cancer it will be due to the years living under the desert sun.

Related: How much radiation is an airline pilot exposed to in a year?

Related: Are sun's UV rays more harmful on an airplane at high altitude?

50% of radiations in excess... which type of radiations? I wouldn't care too much about UV, but ionizing cosmic rays are a bigger issue. Cosmic rays are not blocked by the aircraft skin, and less than 1 mSv is allowed for an unborn child (1 mSv / year). Airlines prevent a pregnant crew member to fly at high altitudes.

@mins I know more than a few pilots that flew until 8+ months until taking maternity leave. the airline didn't care as long as you were medically fit and weren't due within a week.

@casey: EU countries monitor and protect: EU guildeline (Council Directive 96/29/EURATOM of 13 May 1996), and local implementations. Comparison US / EU. There is also a FAA software to evaluate exposure.

Perhaps an aircraft design that stores fuel above the cockpit could mitigate radiation. Not unlike spacecraft concepts that store water around crew quarters.

Broadly speaking, radiation exposure can be mitigated in three ways: Time, Distance, and Shielding.  Two of these mitigating factors can't really be improved: Distance and Time.
For distance, the radiation exposure concern for commercial jet pilots (and travelers)is generally related to cosmic radiation and ultraviolet radiation from the sun. The sources are already quite distant, and the practical distances we can achieve on Earth won't make any appreciable difference here, so we can neglect distance.
Time (duration of exposure) is already somewhat limited by the duration of flights, but the cumulative effect over multiple flights is what we're generally concerned about when we discuss "pilot's radiation exposure".
As their career requires them to fly, and the nature of jets means they'll be flying at high altitude there's not much that can be done with time, except perhaps having a very short career or not accepting a large number of flights. These options are not economically attractive if flying is your career.
That leaves shielding. Pilots sacrifice the benefit of shielding (from the Earth's atmosphere) as they climb: The atmosphere is less dense and there is less of it between the pilot and the background radiation, therefore their exposure is increased.
It's here that improvements can at least theoretically be made: The pilots and passengers already gain some shielding from the structure of the aircraft, but not nearly as much as 30,000 feet of atmosphere provides. The aircraft could be constructed with additional radiation-shielding materials (lead foil for example, and UV-attenuating tints in the windows) but doing so would add a significant amount of weight.
As with most radiation shielding situations it ultimately becomes an economic trade-off: You implement shielding to bring the exposure (dose) down to an acceptable level given the time and distance constraints you're working within.
The additional dose received by pilots is already extremely low, and adding shielding to reduce it further would not give a huge increase in safety. The costs (in terms of aircraft design, construction, and operating cost to carry the additional weight) would exceed the cost of treating the relatively minor complications such as skin cancer which may result from the additional exposure over a lifetime career of flying.

If all of that was too much to read, the short answer to your question is "The best way to mitigate increased radiation exposure from flying is to remain at low altitudes." (Similar to how the best way to mitigate the increased radiation from living in Denver, Colorado at ~5,000 feet above MSL is to move to New Orleans, LA at 7 feet below MSL.)
The next best thing would be to fly less frequently or on shorter legs (to reduce the duration of exposure).

"Tinting" windows is pointless.  Normal window materials block UV.

“the relatively minor complications such as skin cancer” I’m not quite sure everybody would qualify it like that…

Looks like the question is about UV radiation. If the cockpit is closed, there is no need to take any special action for protection as this radiation does not penetrate plexiglass windows of the aircraft. There is a good, extensive answer here.

Got 3 commercial pilots in my family, they all say the same thing: sunblock lotion if possible when bare arms are exposed. Although commercial pilots often wear a full suit, they do commonly wear a short sleeve shirt underneath a bog-standard jacket. My sister has resorted to wearing one of those "sporting arm sleeve" things for extra protection.

"sunblock" or sunscreen are completely useless if you are behind a window.


text:
What do these polygons mean on VFR charts?
There are a lot of blue polygons on this VFR chart:

What do they mean?
Source

Could you link to the actual chart or a higher resolution image so that we may zoom in and read the text that is on the chart?

To add a little to @abelenky's answer, you'll notice that each area has a identifier in it: SBR-522, SBP-505 etc. Those identifiers are made up of the ICAO country prefix, the airspace type, and a unique code. The airspace type can be Prohibited (P), Restricted (R) or Danger (D).
Since SB is the ICAO code for Brazil, SBR-522 is Brazil Restricted area #522; SBP-505 is Brazil Prohibited area#505 etc. I couldn't quickly see any nearby danger areas, but here's one in South Africa: FAD-193, near Port Elizabeth.
You can look up those codes in each country's Aeronautical Information Publication (AIP) or local equivalent to get more information about what each area is, what altitude it goes up to, any special rules etc.

To add to the informative answers already here, this chart excerpt is from SkyVector.com and depicts a World VFR chart of this area in south-eastern Brazil.
Where available, SkyVector uses FAA sectional charts to stitch together their World VFR product. Where those are unavailable, my understanding is that SkyVector uses other available data to create their own charts. See this excerpt from a SkyVector product announcement (emphasis mine):

World VFR
This chart is a "Sectional-style" VFR chart for use at low levels. For
  the United States, official FAA charts have been thoughtfully stitched
  together. For the rest of the world, topographical and aeronautical
  data have been sourced and assembled in a very high quality rendering.

Where SkyVector has used available FAA sectional charts, all chart depictions and symbology are provided by the FAA and follow the FAA charting guidelines laid out in the Aeronautical Chart User's Guide (Aero Guide) that @abelenky linked to in his answer. See this Aviation.SE answer for more information on that document and it's availability. Within SkyVector some of the same information can be found on individual sectional chart renderings.
Now, this is speculation on my part, but I understand that where SkyVector has used other topographical and aeronautical data to assemble World VFR charts outside the United States, they have chosen to use the same depictions and symbology for those charts. For this reason, the Aero Guide should be useable as a guide to understanding those renderings as well.

See Page #10 of this document, which indicates that the markings show "Prohibited, Restricted and Warning Areas"


text:
Why do some aircraft stay in airports for a long time?
Some aircraft used in long-haul flights arrive at the airport daily at 10 am and stay there until 7 pm. Why do the airlines send their planes and make them stay in the airports for more than 9 hours every day?

Overhaul and inspections and many other reasons.

Local curfew can prevent a long haul flight from departing because the flight must arrive at the destination outside the curfew period.

There are many reasons. At least one is that the airline may not need that airframe type until later that day (the next flight that requires said airframe). Airlines don't just fly any plane they have on any route they have, this would be terribly inefficient and involve using an airplane that is not needed for a given mission. Take any major airline for example that fly large planes to lots of destination in Europe. Lets say that they have a 777 Arrive at EWR from Paris. The next long haul flight that airline has out of EWR is that evening to Dublin. But though out the day the carrier has 2 commuter flights down to Charlottesville VA totaling about 100 passengers between the two flights. They are not going to use a 777 to move 100 people and some light bags, so the plane sits until its needed again.
All planes (even non commercial) are built for a given "mission" much like you would not buy a Ferrari if you wanted a car that was good on gas.


text:
What are these green "bags" on the SSJ100?
I've seen some green "bags" on the SSJ100 when they were building it. What is the purpose of these?

Looks like it's probably sound proofing/insulation/fire barrier material.

Text attached to this image in the original article: "The fuselage of the aircraft from the inside is lined with green mats for thermal and acoustic insulation Photo: Alexey Petrov"

That's cabin insulation - probably fiberglass.
It's not always in green bags (blankets), and not always fiberglass, but some kind of insulation is necessary to help control temperature and reduce cabin noise (air moving over the fuselage is REALLY loud).
Here are some other photos of different types of insulation:

Basic fiberglass with a plastic backing, cut to fit.
Fiberglass with either plastic or foil backings is commonly used because it is both light and inherently flame-retardant (as long as the backing is fireproof it will not burn).

Soundex - a sandiwch of acoustic foam, thermal insulating foam and aluminum foil - is a popular choice on propeller aircraft: Slightly heaver than fiberglass, but better at dampening sound.

Foam padding (similar to the foam used under carpets) does a decent job at both sound and thermal insulation. In this case it's green & has no covering, but colors and coverings vary.

Prefabricated insulation blankets on a Boeing 777.
(I believe these are fiberglass sealed in polyethylene, they're manufactured to fit each bay without cutting which avoids loose insulation material floating around).

And do they act as fire insulators also?

Is there ever a chance to hear the REALLY LOUD air over fuselage sound?

@curious_cat In a glider, sure. Much of the ambient white noise you hear on jets is also from wind noise (as opposed to engine noise). In propeller-driven planes the propeller noise typically dwarfs the wind noise.

@kepler22b While the insulation material is not flammable (by regulation) I would not expect it to be a particularly effective fire stop: It will delay heat propagation for a time, but its primary purpose is to reduce noise and keep the cabin warm and relatively quiet. (The FAA has done some studies on what happens when you try to burn aircraft insulation under conditions that might be found in an accident, the reports make for interesting, if technically dense, reading)

@voretaq7 But are gliders relatively quiet you would say or not at all? I've never been on one sadly. For example, on a scale of 1 to 100 (noisiest) if you had to rate a glider vs 747 vs prop plane how would they rate?

@voretaq7 Of course, to do this right one must have no sound insulation in the jet. Also, is there a common speed all can fly to do an apples to apples comparison?

@curious_cat comparing average Interior sound levels (for say a glider, a helicopter, a piston single, a piston twin, a turboprop, and a jet) would probably be a good subject for a separate question - only because I don't know the answer offhand and expect it would take a little bit of research to turn up reliable sources :)

@voretaq7 Done! See here: http://aviation.stackexchange.com/questions/25151/relative-noise-levels-in-various-aircraft-scenarios

@curious_cat Skydiving airplanes typically have all interior panels and insulation removed too, in order to save weight.  This saves the operator money and gets the jumpers to altitude faster!

@Lnafziger . . . but skydivers are just cargo with a short shelf-life anyway. That's why the FAA allows them to sit on the floor: They don't need comfort and safety, they're jumping out of the airplane anyway!

@voretaq7 They still need safety at low altitudes!  ;-)


text:
Why do pilots need the ceiling, time, and dew point in the ATIS?
For example:

Ceiling: what is the ceiling? Why do they need to know the ceiling?
Zulu time: what is the zulu time?
Dew point: why do they need to know the dew point?

The ceiling is the lowest altitude where clouds cover more than half of the sky. This is important because climbing above that altitude means you will most likely have to fly through clouds. This makes navigation more difficult and pilots are required to have special training to fly in low visibility. If the ceiling is too low, pilots can't be at a safe altitude above the ground and out of the clouds at the same time. Low ceilings are also critical for landing, and may require pilots to make an instrument approach and landing.
Zulu time refers to UTC time, which is the universal coordinated time. Zulu or UTC time is helpful as a worldwide reference in fields like aviation, to avoid issues like dealing with changing between local time zones. The ATIS will contain the Zulu time of the latest official weather observation (the hourly METAR or as-needed SPECI based on changing weather conditions).
The dew point in relation to the temperature gives the pilots information about the humidity, and can affect visibility. If the dew point is close to the temperature, humidity is high, which can cause hazy conditions, or even fog. As with the ceiling, this can warn pilots of possible changes in conditions that will make it harder to see the ground or other aircraft while in flight. In terms of aircraft performance, the dew point is also needed to determine the true density altitude, when combined with the pressure and temperature. A high dew point means a higher density altitude, which reduces aircraft performance.
Dew point is also very important in certain helicopters with carburetors, like the Robinson R-22 and R-44 helicopters, which are subject to carb icing even during take-off because they only use as-required power rather than full throttle. In this case, carb heat needs to be applied whenever the temp/dew point spread is 15C or less. Here is the citation from the R-22 POH:

BTW, if you hover over the time of a question, answer, comment or edit on this site, you'll see the Zulu date and time...

Can dew point be useful for anything else like performance?

@Andrius I think that historically, surely. Even your car has a higher fuel consumption in humid weather.

Note that the time should not play a role primarily, you simply receive the latest weather report and that should be the current one. It's there as quite a security measure against information chaos, a sort-of double-check.

Piston airplanes with carburetors are also subject to icing in the same conditions as a helicopter, and they contain POH procedures to mitigate.  @Andrius humidity does change the performance, but not enough that the FAA requires compensation for it.

The temperature/dew point spread also predicts where a ceiling could develop, even if one isn’t present right now.

Dew point can most certainly be used for performance. High humidity can cause a longer take off roll.
When combined with a high altitude airport and hot temps, it can be a struggle to get airborne.
Cooler, less humid air is more dense--there's more "air" for the wing to bite into. So, a pilot listening to ATIS would want to know the temp, dew point, and temp for the airport to determine (in this example) takeoff roll distance.

would you care to add some more details to your answer?

Humidity is not part of the runway distance calculation

To add to the above, in all carbureted A/C dew point is needed for indication of carburetor icing.
Dew Point relative to temperature is a useful indication of weather conditions .

authors: Валерий Юдичев


text:
What are these markings on the runway at Haneda Airport?
I haven't seen these markings in other airports in the world. Look:

They also appear in other Japanese airports. What do they mean?

I dug around for a while but couldn't find any official documentation on this (I suspect someone whose Japanese is better than mine will have to do that.)
But!  I did find the markings on all of the Haneda Airport runways and I noticed they were roughly halfway along the length of the entire physical runway.  A little bit of measuring confirmed my suspicion, it appears the marks show you exactly where the halfway point is on that particular runway.
I also looked at other Japanese airports and took measurements of the same markings at Narita, Osaka and Kobe.  All airports turned up the same results.  (You can use the measure tool on Google Maps to confirm if you'd like to)
I also find out that not all airports in Japan have these markings.  Neither Nagasaki nor Osaka seem to have markings like the ones mentioned above...
Not sure why they mark the halfway point...someone with better Japanese than me will have to look into the history of that decision.

Edit: mins found some documentation and posted it in the comments (thanks mins!):
This is an English translation of a report done by the Japan Transport Safety Board regarding a runway overrun.  They mention the meaning of the markings (in passing) on page 2.
Here's a capture mins created of the relevant part of the report:

So, there we go, more than just circumstantial evidence we have the aviation authority of Japan saying it's true.  It's the halfway mark for the runway.

You beat me to this! I even called the number given on this site - http://www.mlit.go.jp/en/index.html - only to find myself with a Japanese automated message.

"Not sure why they mark the halfway point...someone with better Japanese than me will have to look into the history of that decision." - Probably for the Captain to tell his FO "You gonna stop or what?"

I can't think of a good reason to have them.  Perhaps that's why they are not used in other countries.

@Simon Apparently they can help reduce overrun accidents.

Marking also indicated in the official AD chart of Sado/RJSD airport.

authors: Шахбоз Яхшигельдиев


text:
Why are the tips of the flap track fairings painted red?
The fairings are painted red at the tips, look:

Source: Airliners.net
I have seen that on many new airplanes, not only the A330. So why are they painted red?

So the dude maneuvering the baggage conveyor or the scissorlift for the cabin food will not hit them?

@mins I take it from the question mark at the end of Peter's comment that he's not sure. The question is still not answered

@mins I suspect SMSvonder Tann's now-deleted answer may have been correct, as the A-330-200 shown in the photo was the first -200 off the line.

@TomMcw I don't know if SMSvonderTann's answer applies. Look at the photo of the 777 on the question talking about spoilers. It has the tip of the fairings painted red and it is not new or being tested

@kepler22b I see. It also looks like the red paint is kinda slapped on that 777. Peter could be correct. It's just that he put a question mark at the end indicating it was just a presumption. Should the question not remain unanswered until someone can verify?

@mins looks like they must have problems with people running into them. Darn tug drivers! I'd never be that clumsy! ...ahem! OK, so I might have aaaaalmost hit a DC-10 once.  But it wasn't my fault!

@mins A-380 is a bull in a china shop!

Elaborating on Peter Kämpf's comment: The flashy tips are for preventing accidents during ground handling operations, e.g. by belt loaders. This can be a painting or an adhesive tape (possibly reflective, useful at night).
According the pages referenced below, this is done for the A320 family aircraft for which the flap track canoe fairings are not low enough to be obvious, not high enough to not cause a problem.
It seems this is a company decision not required by regulation. Several airlines do it.
Variations on the painting (taping):

Only the fairings close to the locations where ground handling personnel works.
Only the right side of the aircraft.
Also the winglet.
Color used: Red, bright pink, reflective green.

Photo Taha Ashoori on Airliners.net (source)

Photo Vin Lane-Kieltyka on Flickr (source)

(Source)

References (non authoritative):

Air Canada Flap Track Fairing Speed Tape? (Airliners.net).
Why Do Airliners Paint Trailing Edge Flap Fairing (Airliners.net).
Colour On Flap Track Fairings (Airliners.net).

When Southwest Airlines started flying Boeing 737 Next Generation, many years ago, now, they used the same red as on the underside of their "Corndog" scheme for the flap track fairings of the NG models. So ground crew would easily know whether they were receiving a "Classic" or an "NG".


text:
In fighter jets, is the minimum speed calculated with the flaps in the down position or up?
I asked that question because F16 flying straight and level at minimum speed does not have flaps down.
So how is the minimum speed calculated by aircraft designers?

This isn't very clear and doesn't fully agree with the title.  You should edit the question to make it clearer what you're asking, then edit the title to match the question.

In any aircraft where the flaps produce lift the minimum speed will be achieved in a flaps down configuration.

Whoever downvoted me without leaving feedback, is my answer incorrect?  It is a short simple question, it deserves a short simple answer.  P.S.  I am answering the question in the bold headline.  "How is calculated" is a separate question...

But some jets (F16 in special) in slow flight demo's don't lower the flaps  when the landing gear is up. That's why I put that question?

In doing a demo like that, having flaps down creates a high drag condition that can make the maneuver more risky, say, if thrust gets too low or you hit a bit of reduced performance wind shear at a few hundred feet, so it's done flaps up, at the minimum speed appropriate to flaps up, because it makes recovery from a low energy state much faster.

"Why do some fighter jets perform a slow flight demo with flaps up rather than flaps down?" is not the question you asked.  You need to be clear about the information you are seeking.

@MichaelHall Across Stack Exchanges, it's generally suggested not to answer a bad question.

@Zeiss Ikon - I wouldn't characterize the question itself as "bad".  Poor grammar perhaps, but the main portion I chose to answer was straightforward enough.  The problem is that the question keeps morphing, and there are now actually 3 questions:  Is min speed calculated with flaps up or down?  How is min speed calculated? and Why do some fighter jets perform slow flight demo with flaps up?  OK, so maybe it is actually a bad question then...  ;)

Sorry for my grammar mistakes, my English is very poor, I learned   only in  high school and don't used to often (only  on forums , Facebook, and there's no  problem if you don't have good grammar, as you know). The F16 demo  topic was the first thing I had in mind when I put the problem here. Because the minimum speed for the F-16 is without the flaps down,When you put the flaps down the landing gear go down the nose tends to go down(so the AOA will be reduced)


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In F-16 the pilot or the FLCS , deflect the rudder to correct the adverse yaw effects in direction of roll during an aileron roll or in opposite way?
Is the  rudder moving by FBW in direction of roll or in the opposite direction?
I understand that the rudder is used due to the ARI system (ailerons - rudder interconnect), but don't have any idea how much or in what direction it is used throughout the process ?

I struggle to understand what you're asking... Are you asking if you need to use the rudder (but on an FBW aircraft is a tricky question...) during an aileron roll to compensate for adverse yaw on the F-16?

Exactly. I understand that the rudder is used due ARI system (ailerons - rudder interconnect), but don't have any idea how much or in what direction is used, or only if barell rolled the rolls and pulling some G's. Some pilots tell me that no rudder another's tell me the rudder is used in slow flight only.

I still do not understand if you are asking about whether the pilot needs to manually input rudder commands because the FCS does not always provide correct rudder inputs, or if the rudder is needed at all, through pilot or computer inputs. I have heard and read that an F-16 pilot may not need to touch the rudder for 90% of a mission, but that is because the FCS does it for them, not because the F-16 does not usually need rudder deflection.

Only " if the rudder is needed at all, through computer inputs" and direction in which is deflected.

@GeorgeGeo The control laws will generate the rudder input. Generally it's to generate a stability-axis roll and minimize adverse sideslip via feedback and feedforwards. The actions may be counter-intuitive some times to achieve the desired results.

Adverse yaw from aileron deflection, at roll initiation, is a function of wing span: a longer wing span creates more adverse yaw. And a long wing span is not what an F-16 possesses.
Image source
Its main problem at lower airspeed is creating a roll rate at all with such short wings. Deflecting the rudder may help increasing the roll rate - for a left roll, it would be deflected Trailing Edge Right, creating adverse yaw. Which might or might be compensated by asymmetric aileron deflection, depending on the priorities posed upon the manoeuvres of a fighter aircraft at low speed. Of course, it makes much more sense to deflect the horizontal tail such that it helps in the roll.
At high roll rates, adverse yaw is created by the difference in local angle of attack at left and right aileron. Plus an aeroplane with low wing span will start to nutate: it wants to spin about its rotation axis with the highest moment of inertia, so tends to want to convert roll into pitch from inertial coupling. So high roll rates are a different kettle of fish in aeroplanes with short wing span, with lots of work to do for the fly-by-wire computers.

In the F-16, is rudder used to arrest the adverse yaw effects...

Most probably not. Adverse yaw from aileron deflection is not a large issue on fighter aircraft.

In normal positively-loaded flight in the F-16, we can be sure that when the pilot moves (presses) the control stick to the left to give a left roll input, the computer does not move the rudder to the right.

Not true. IF IT FLY SLOW that is what computer do

You mean, the opposite of what I do in a sailplane? Are you sure about that?  Why?

To keep the nose above the horizon line. But only at the slower speed. But it is done by FLCS not pilot itself. And if is put the negative G (unload) doses the same way at any point in time and at good maneuver speed.

I am skeptical about this.  You are saying that the computer commands a sideslip to keep the nose up?  Do you have a source?

As an aside, note that a high rate of roll around an aircraft's longitudinal axis tends to automatically convert angle-of-attack into sideslip, even in the absence of any aerodynamic adverse yaw torque.

You talk about roll coupling here


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Is there a difference from alignment with the fuselage between J79 and Spey engine versions used in the F4?
Is there a difference between the J79 and Spey engine versions used in the F4 Phantom in terms of alignment with the fuselage? It looks to me like the Spey nozzles are pointing downward.

Are you asking if the engines are different from each other (eg J79 vs Spey) or if the engines are different from the design standard (eg J79 in the F-4 vs J79 in the F-104)?

I'm asking if the engines are different from each other  J79 vs Spey.

Oh, childhood memories! I used to build scale models as a kid, and always wondered about the weird alignment of the Phantom's nozzles. Not sure which version I had built then though.


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When F/A-18 landing on the carrier the main landing gear touching the runaway first or the hook?
The hook in my opinion must be lower enough to make sure that he gets the proper cable, but it is possible that I'm not right.

Please don't downvote without leaving comments why. The question title seems perfectly clear, even if the question body is garbled. Does the downvoter think this is a poorly posed question? Or is the body text the problem? If it's the text, why not fix it instead of downvote?

Yes, in a properly flown approach at the correct attitude the hook touches down first.  Look at photos and video to verify.
Not just the F-18, all carrier aircraft are this way.  (although the carrier airwing has become a lot more homogeneous than it was in years past...)

In level flight , but not in the landing pattern, just straight away, with the hook down and landing gear the hook is at the same level as the wheels or much lower?

In level flight, the end of the hook hangs pretty close to straight down, so it simply depends on the length of the hook, the length of the landing gear strut, and the Angle of Attack. The slower the aircraft is, the higher the AOA, and the lower the hook will be.


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If pilot use rudder to roll the aircraft at high AOA in the F4 Phantom then one aileron from one wing and one spoiler from other will be deflected?
I have heard that the F4 Phantom pilots can make barrel rolls at lower speed /higher AOA. They use only rudder deflection and keep the stick column centered (left /right wise)-only pull onto the belly to have the G's- to prevent adverse yaw effects. Does the spoiler on top of the wing move during the maneuver if the aileron stay neutral? The way it works for level rolls is : one side aileron deflected down but the other one is not (there is some slat(spoiler) on the other wing to assist the aileron down deflection. Is there a built in type of assistant like ailerons - rudder interconnection to help maneuvering? Or do the wings remain clean with no deflection of the control surface?

of course it depends upon the situation and the specific fighter. when maneuvering at high angles of attack and high G, I always used solely aft stick and rudder, never any aileron or spoilers input. Sometimes I would use full rudder, all the way to the stops. Other times, not so much.

"When the F4 Phantom pilots makes barrel rolls at higher AOA, they use only rudder and keep the stick column centered."
Where does that come from ? It seems highly confusing to me, are you sure you didn't mix things up ?

I'm sure. There's two ways to do that :1 the traditional way - pull up then deflection of the stick  left or right and a bit of rudder, this is for higher speed or lower AOA. 2the pull up, stick in middle (not letting stick to slip out - left or right - by squeezing the knees together,- this was tell me by  a pilot-), but pulling toward your belly and pushing the rudder. This is for low speed and subsequent higher AOA. My question is not about that, it is about the aircraft surfaces deployment when the only rudder and pulling from elevators.

The second option you're describing is not a barrel roll but a snap roll which is actually a spin carrying a lot of forward speed.

I don't think he's describing a snap roll.  A swept wing with dihedral tips will certainly exhibit aerodynamic coupling between yaw (or more properly sideslip) and roll, and this effect will be most pronounced at high angles-of-attack.  Needs to be developed into a proper answer, but I'd have to find appropriate sources as I'm no expert on the F-4.

where does that image come from? and that citation?

The first thing you need to fix, which may get some of the DV's removed, is the idea that the slat is a surface on top of the wing. That's not what a slat is. The deflected surface shown in your photo is a spoiler or spoileron. I don't know whether the F-4 used differential spoiler deflection (i.e. spoillerons) as part of the roll control system. Your basic question seems to be, in part, whether surfaces on the wings automatically deflected whenever the rudder was deflected; the answer is almost certainly "no"

Yet your idea that rudder inputs should be used for roll control in the F-4 at high angles-of-attack may be a sound one, despite the apparent skepticism of other ASE members. See for example https://simworksstudios.com/knowledge-base/f4bn-chapters/general-information-specifications.html . Yes, it is just a link from a sim (game) page, but similar sources might be found in reference to the real thing. And it's pretty clear that a "snap roll" is NOT what is being referenced here. Note the reference to aerodynamic coupling between slip and roll in the link

Also, yes, the citation at the end of your question needs a source. Is it from an experienced military flier? A gamer? ?? PS The F-4 did in fact have slats at least in some models but that's not what is shown in your photo. And they were certainly not automatically opened whenever the rudder was moved. As to whether they ever opened differentially-- probably not, they were probably hydraulically driven and always opened together at a certain airspeed or angle-of-attack, or perhaps at a certain flaps setting, etc.

Probably enough there for a real answer but I'd like to give him a chance to fix the question first  PS I see an edit has already been made, good-- more later.

quiet flyer, Yes my mistake it is called spoiler. The citation is from a real pilot, not sim buff. But you wrong about the symetrical deployment of the spoilers. Just look at the F14Tomcat, F4E, orG.

No, I'm not saying that spoilers always deploy symmetrically.  I'm saying that I don't know whether differential spoiler (spoileron) deflection was used on the F-4 (I'd guess probably it was, but connected to aileron inputs only, not connected to rudder inputs), and I'm also saying that the actual SLATS were probably not allowed to move differentially and were certainly not physically interconnected either to aileron inputs or rudder inputs.

PS just as an added point of reference, in some older aircraft such as Bf-109 the actual SLATS were purely aerodynamically driven and sometimes one would open when the other was still closed.  I highly doubt this was the case with the F-4 though.  That might help make my comments more clear.

Live aside slats, from the front of the wings (leading edge), for F4are symetrical deployed. Anyway for F18 Legacy Hornet if rolling then they would be asymmetric  deflected just for to know about it. My question was summarised by you. Maybe in sim are some filters to cancel (dumping) the rolling momentum from the tail. That is why I asked.

The F86 Sabre, A4 Skyhawk they have same gravitational leading edges deployment (slats),jamming from time to time. My guess is that the yaw moment (drifting) will do that jamming.

A Barrel Roll is a maneuver where the aircraft flight path follows what would be the surface of a huge horizontal barrel in the sky. To do this you of course need to roll the aircraft. To roll the Phantom, no matter what maneuver you are attempting, requires that you create differential lift on the wings. (more lift on the up-moving wing than on the down-moving wing). At low angle of Attack (AOA), in any model of F-4, you use the ailerons/spoilers to do this. At higher AOA, the ailerons would induce adverse yaw, and therefore you need to create this differential lift by yawing the aircraft with the rudder (since it's a swept wing aircraft). As AOA increases above 10-12 units, the pilot needs to blend in more and more rudder, and less aileron, until at high AOA (19 units in early non-slatted aircraft like F-4B/C/D), he is using rudder exclusively. In later slatted aircraft (USAF F-4Es, F-4Js, USN F-4J/S, etc.) this effect was somewhat mitigated by the slats (they energized the airflow over the top of the wing), and the pilot could use some aileron throughout the AOA range, (but still less and less as AOA increased), all the way to 25 units AOA.
As to your other question about slat deployment, this happened automagically, based on AOA, at about 12-14 units AOA as I recall. And then would retract when AOA fell below 10-12 units... No pilot input was necessary.
So, in the execution of a Barrel Roll in the F-4, starting at 450 KIAS and low AOA at the entry point, the aircraft would climb and descend 4-5000 feet, and  slow to somewhere between 200-250 KIAS and higher AOA at the high point, and then accelerate back to 450 KIAS and low AOA at the completion of the maneuver. As a result, the need for aileron and rudder to effect the roll continuously and gradually changed throughout the maneuver.
NOTE. (to address comment made in the question relating to photograph). The F-4's ailerons did move up slightly when the stick was deflected towards that wing, but at high AOA, the aerodynamic effect was negligible due to the wing blanking the airflow back there. SO the F-4 also had spoilers on the top of the wing that would deflect upwards as well, both to decrease the lift on the wing and cause a roll in that direction, and to add drag on that wing to balance the drag from the down aileron on the opposite wing. The control surface deflected on the upper wing in the photo is the spoiler, caused by the pilot pushing the stick to the left.
The following is from the USAF F-4E flight Manual:

Pretend that not everyone here is a pilot. What is a "unit" of AoA? Is it a degree, some percentage of max elevator deflection, something else entirely?

In the F-4 AOA was displayed and referenced in all manuals and documents in arbitrary "unit"s, which represented the actual AOA angle. The relationship between AOA units and AOA degrees, or radians, or Milliradians was not specified. We were only taught the relationship between the units and the aerodynamic properties that the aircraft at various AOA values, Un-loaded (very low AOA) was 3-5 units, L/Dmax occurred at 10-12 units, Cl max (Max performance or approach AOA) occurred at 19.2 units (non-Slatted) and at 25 units (slatted). Stall (loss of directional control) occurred at 23/29 units.

... and my apologies for not "pretending"... I've never been good at that... otherwise I might "pretend" that not everyone here was polite....  oh wait, they're not...

Thanks for the info. That strikes me as odd that they would use "units" and not something that people would come in with a basic understanding of. Most people can reasonably guestimate 15° or 30°, but 25 "units" has no built in human intuition point. OTOH, maybe that's why they went with it...

no worries, I added the explanation from the USAF F-4E flight Manual. It appears that the units, from 0 to 30 "units" represent angular rotation of the AOA probe from -10 to + 40 angular degrees. How that aligns with actual AOA is of course ALSO arbitrary, as it is a measurement taken from the arbitrary line of the mean aerodynamic chord (MAC) of the main wing.

They are 3 different ways to roll an airplane:
First the barrel roll during which the airplane is flying normally, you are keeping positive g rate and using ailerons to induce the roll. The trajectory is making a wide spiral and you use rudder input to keep the symmetry of the flight.
Second the aileron roll, where the aircraft continues in a straight line and your airplane is almost rolling on itself, the roll rate is dependent on your ailerons input and you use rudder to displace the nose of the aircraft around the central axis by mostly crating lift when your roll position is equal to 90 or 270°.

Finally and that is what you are describing is the snap roll or flick roll. Which is basically a horizontal spin. flying low you simultaneously apply full rudder deflection and pull the yoke. This means you have high AOA and non symmetrical flow inducing a spin by stalling one of the wing. But you have enough forward momentum to continue in a straight line, thus making it looks like a roll. Once the snap roll initiated, some aileron might be needed to either keep or stop the rotation but as for a normal spin this might change from one aircraft to another.

True, but I asked about the F4 only-there's something ( a system maybe that couples the rudder with slats)? That's all?

A mechanical link between rudder and any control surface on the wing doesn't make sens as they are supposed to work around two different axis. What exist are yaw damper that replace rudder input in coordinated turn and electronics. New military aircraft have combined control surface deflection to increase maneuverability and the flight performances of the aircraft. But that's the onboard computer doing it and I don't think this apply to the F4

I asked because in some simulator the opposite slat lifted a bit(3degrees) and along with the aileron if  rudder deflection to cancel any little disturbance from the level flight.

I think the categorization of rolls into 3 types is somewhat arbitrary.  For what you are calling the "aileron roll", you are saying that the rudder is used to create sideways lift at 90 degrees and 270 degrees.  Does it not also follow that forward stick should be used to create negative (skyward) lift at 180 degrees?  But the diagram you posted doesn't show the aircraft in a nose-high attitude when inverted, nor does it show it in a nose-high attitude at 270 degrees.  (The attitude at 90 degees isn't illustrated.) (ctd)

(....ctd)  I think most pilots would consider an aileron-roll to be a positively-loaded maneuver, just with a higher roll rate, less time to complete, and less variation in G-load and aircraft attitude and trajectory than a "barrel roll".  Meanwhile your description of an "aileron roll" really sounds more like a "slow roll"-- which in theory could be completed at any roll rate, slow or fast, but the key point being that the aerodynamic force vector / G-loading continually points in the skyward/ earthward direction, rather than "upward"/ downward in the pilot's reference frame.

For more on the same theme see https://aviation.stackexchange.com/a/66561/34686 , which is an answer that I forgot I had written but just now searched up.

@quietflyer it all depend on the aicraft speed, the diagram is good for an extra330 where you don't even need rudder during the roll, due to higher speed and roll rate. But in a slower airplane the Cap-10 for example you need rudder on the side and forward stick while inverted. The -1g you will experience it in both aircraft just not for the same amount of time. At least it is the strict definition I know from my aerobatic flying. The barrel roll can be done with any aircraft if your a good enough pilot but not the aileron roll.

Yet another variation-- I took some dual aerobatic lessons in a glider, where we did what we called "aileron rolls" (I think) or maybe just "rolls" and we definitely did push the stick forward to create negative G when inverted, but we used the rudder only for coordination (to keep the yaw string / ball centered) and not to create any sideways lift.  The roll rate wasn't real fast, it was a purpose-designed aerobatic glider but I'm sure the roll rate was slower than say a Cap-10.  Lots of possible variations on the theme it seems to me...  Oh well probably shouldn't have typed so much...

Well... you mixed a bit both of the solution there and I see two reasons. A glider don't fly on the side, in opposite to modern aerobatic aircraft that have fuselage lift and then they don't really like non-symmetric flight condition. To initiate the barrel roll you start to pull straight to put the nose up 30° and then roll, keeping the yoke pulled to ensure positive g rating all the way. But you end up with a nose down attitude: In aileron roll your nose is actually making a circle on the horizon and the slower you fly the bigger the circle. But most important your altitude remain constant.


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What is the purpose of fins on the empennage on some helicopters?
The S-70 Black Hawk has some kind of movable surfaces on its tail, look:

Source: Airliners.net
They look like "elevators" on airplanes. Does anybody know what are these things for?

Related: Can the MH-60 helicopter fly without one or all of the stabilators?

Curiously, a variant of this is used for presidential transport by the Marines.

I had a pretty good idea once I looked up what an empennage is.

It's a stabilator used on the Blackhawk to reduce attitude changes with airspeed and to offset pitch effects from the tail rotor.  It's part of the automatic flight control system.
All "traditional" design helicopters have horizontal stabilisers to push the tail down to reduce the nose down pitch in forward flight.  Fixed ones are normally trimmed to provide a more level deck at typical cruise speed.
On the Blackhawk, it's fully movable. It is automatically adjusted according to collective pitch and airspeed. From here, the benefits are:

Align stabilator and main rotor downwash in low speed flight to minimize nose up attitude resulting from downwash.
Provide collective coupling to minimize pitch attitude excursions due to collective inputs from the pilot.
Decrease angle of incidence with increased airspeed to improve static stability.
Provide sideslip to pitch coupling to reduce susceptibility to gusts.
Provide pitch rate feedback to improve dynamic stability.

Not just on later models.  It was that way on the A.


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What is the purpose of eyebrow windows?
Nowadays they are no longer needed but why do they cover them up like in this photo?

What is their purpose and why aren't they used anymore?
Source

They are mentioned in this discussion about cockpit windows

Can you please circle what you are talking about for future readers who may not know what that is?

Wikipedia answers this on the Boeing 737 page:

Most 737 cockpits are equipped with "eyebrow windows" positioned above
  the main glareshield. Eyebrow windows were a feature of the original
  707 and 727. They allowed for greater visibility in turns, and
  offered better sky views if navigating by stars. With modern avionics,
  they became redundant, and many pilots actually placed newspapers or
  other objects in them to block out sun glare. They were eliminated
  from the 737 cockpit design in 2004, although they are still installed
  at customer request. These windows are sometimes removed and
  plugged, usually during maintenance overhauls, and can be
  distinguished by the metal plug which differs from the smooth metal in
  later aircraft that were not originally fitted with the windows.

All of that except the "navigating by the starts" comment sounds about right.  Celestial navigation is done with a sextant, which needs a dedicated sextant port -- not through aircraft windows.  You most certainly are NOT "following a star," because unless you're pointing at Polaris, you'd be following a star that's moving in the sky!

@RalphJ: Worth pointing out that the article no longer makes that claim - indeed, it does the opposite.

To add to Steve's correct answer, Boeing has historically designed aircraft with less than ideal visibility for the pilot. Case in point: Their first all-metal passenger aircraft, the Boeing 247. Its design was ahead of its time and prompted TWA to convince Douglas to build the DC-1 and -2, but was marred by two details: The wing spar was not below the cabin floor level; instead, Boeing expected passengers to climb over the spar on their way to their seat. Many airlines were less enthusiastic and rejected the aircraft in favor of the DC-2 and -3, which also offered more seats.
The second detail was the cockpit window: It was sloped forward, so the visibility in the upper hemisphere was severely restricted. In turns the pilots were basically flying blind. The idea was to angle the window glass such that the instrument lighting would not reflect in the glass, but Boeing soon realized that this was creating new problems, and from the 247D on the window was sloped aft.

Forward fuselage of the Boeing 247 (picture source)
When the 247 was offered to Lufthansa, it was rejected for this particular reason. I guess Boeing engineers were very sensitive to get the visibility right after the 247.

Forward sloping glass... it would be interesting to see what that does in a wind tunnel.

@FreeMan: It did indeed increase drag a bit, which was another reason to never repeat this design detail ever again.

I just realized what "glare-shield" probably means now ... I wonder if it was put in Boeing aircraft at about the same time?

I'd always heard that the eyebrow windows were a holdover from the KC-135 fuselage design, where having them was valuable for seeing a tanker aircraft when being refueled. (Most KC-135 aircraft aren't plumbed as receivers, although variants like the EC-135 are.) Wondering if that's accurate, or urban legend.

@RalphJ: The tanker requirement sounds valid. I make no claim that Boeing transferred the experience directly from the 247 to the 737 - there is too much of a gap.

It would be interesting to see an authoritative source for the idea that the forward slope was primarily intended to prevent internal reflections such as from the instrument lighting, as opposed to preventing sun glare.  This had never occurred to me before.

As another comment above may be suggesting, it would be interesting to know if the change to normal-slant windows in later models of the 247 (I seem to recall that such a change WAS made) was accompanied by the addition of a glare shield above  instrument panel that mostly eliminated the possibility of instruments glaring on windscreen.  That infor would be a great addition to this answer or to another related answer focussing more on these early aircraft like the 247.

@RalphJ -- seeing as a EC-135 would surely be directly behind the tanker when taking on fuel, it seems like urban legend.

I'm an MD-80 pilot (they have huge eyebrow windows).  The eyebrow windows were originally used in tight turns to help the pilots align with the runway.  However, nowadays, it doesn't really add that much visibility.  All it really does is just have the sun shine into the pilots' eyes.  I'e usually cover them up with IFR charts, or checklists.  They look cool on the outside.  But they're not great on the inside.  In addition, the more windows you have on an aircraft, the more time you spend cleaning, checking them, etc.  So, by removing the eyebrow windows, some maintenance time was saved.

A major point in removing the 'eyebrow panels' is reduced costs over the life of the aircraft.
Also in most of the aircraft I've been in they're usually blocked with paper or similar for most of the flight if its sunny! I've heard they reduced noise as well but I haven't been in the newer ones yet and what with the rules on jumpseating getting stricter looks like I'll never have the chance!